H adsorption and the formation of alane oligomers on Al(111)

Complementary scanning tunneling microscopy and surface infrared measurements show that H reacts strongly with Al(111), producing a variety of new alane (aluminum hydride) surface species. Alane oligomers, ranging in size from the monomer to 30-mers, form through a sequence of surface etching and condensation reactions. Atomic hydrogen initiates production by extracting aluminum atoms from the surface lattice to create mobile monohydride monomers (ad-Al-H), which predominate in the low-coverage regime. At higher hydrogen coverages, multihydride oligomers form in coexistence with the ad-Al-H. These alane oligomers are more thermally stable, remaining on the surface at room temperature, where they are directly imaged. The mass transfer of aluminum to surface alanes is discussed in relationship to alane stoichiometry. (C) 1999 Elsevier Science B.V. All rights reserved.